JP2004225098A - Composite work roll for cold rolling made by centrifugal casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite work roll for cold rolling of high quality made by centrifugal casting which is produced at lower cost than that of a quenched work roll made of 10% Cr based or semi-high speed steel based forged steel obtained by using an electroslag melting method, and has wear resistance and grindability equal to or above those of the same. <P>SOLUTION: The composite work roll for cold rolling is made by centrifugal casting centrifugal casting machine with a rotating shaft having a tilt angle of ≤30 degrees, and consists of an external layer and a core materials made of spheroidal graphite cast iron. The external layer is made of an iron based high alloy satisfying 0.50 to 0.95% C, 0.2 to 2.0% Si, 0.2 to 2.0% Mn, 0.1 to 2.0% Ni, 4.5 to 8.5% Cr, 1.5 to 4.5% Mo, 0.1 to 1.0% V and 0.1 to 3.0% W. The content of (Cr+2V) in the spheroidal graphite cast iron composing both the shaft parts of the roll is ≤0.70%. Further, the surface of the external layer is hardened so as to be a Shore hardness of ≥90 by stationary induction quenching. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００５４】
回転摩耗試験は、相手材：ショア硬さ９３の５％Ｃｒ系鍛鋼製焼き入れワークロール材、潤滑：灯油、表面状態：研削施工により表面粗さＲａを２μｍ に調整、ヘルツの接触応力：１４５１ＭＰａ 、すべり率：５％、回転数：２×１０^５ 回の条件で試験を行い、 摩耗減量を測定した。
【００５５】
表１に、本発明材、 従来材及び比較材の回転摩耗試験による摩耗減量を示す。 表１に示すように、本発明材は従来材及び比較材よりも摩耗減量が少なくなっている。 特に、 比較材１及び比較材４は本発明材よりもＣｒ含有量が高いが、摩耗減量が多くなっている。すなわち、Ｃｒを多量に添加するよりもＭｏとともにＶ及びＷを複合添加するほうが、耐摩耗性の向上に効果的である。
【００５６】
このように、 本発明材を冷間圧延用複合ワークロールの外層材に適用すると、その目的とする耐摩耗性の作用及び効果を十分に奏することが明らかである。
研削性評価試験は、直径３５５ｍｍ の汎用砥石（ＷＡ１２０）を用いて、実際の冷間圧延用ワークロールの研削をシミュレートした条件で研削を行い、研削後の表面状況（仕上がり粗度及びビビリの発生有無）により評価した。
【００５７】
表２に、従来材、比較材および本発明材の｛Ｃ＋０．１（Ｃｒ＋０．８Ｍｏ ＋０．４ Ｗ）｝量と仕上がり粗度及びビビリの発生有無との関係を示す。
【００５８】
【表２】

【００５９】
この表から明らかなように、 ｛Ｃ＋０．１（Ｃｒ＋０．８Ｍｏ ＋０．４ Ｗ）｝量が１．７０％以下である本発明材は、汎用砥石を用いてもビビリの発生無しに高い仕上がり粗度に研削することができる。すなわち、｛Ｃ＋０．１（Ｃｒ＋０．８Ｍｏ ＋０．４ Ｗ）｝量を１．７０％以下にすれば、ビビリやスクラッチ疵等の有害な研削欠陥を発生させずに、所定の研削粗さに仕上げることができるという良好な研削性を確保できる。
【００６０】
これに対し、｛Ｃ＋０．１（Ｃｒ＋０．８Ｍｏ ＋０．４ Ｗ）｝量が１．７０％を超える従来材及び比較材は、ビビリが発生するとともに低い仕上がり粗度にしか仕上がらず、研削性に劣ることが明らかとなった。すなわち、研削性を阻害する度合いの大きいＣｒの含有量を抑制して、Ｍｏ、Ｖ及びＷを複合添加することにより、良好な研削性とともに優れた耐摩耗性を確保できる。
【００６１】
このように、 本発明材は、 本発明にかかる冷間圧延用遠心鋳造製複合ワークロールの外層材に適用すると、耐摩耗性に優れるとともに良好な研削性を得られるという効果を十分に奏する。
【００６２】
（実施例２）
直径が６５０ｍｍ 以下の小径ロールが大半を占め、かつ外層にＣｒ、Ｍｏ、Ｖ、Ｗ等の白銑化傾向の強い元素を多量に含有することにより芯材の白銑化及び脆弱化が生じ易い、外層の表面がショア硬さ９０以上に硬化された耐摩耗性及び研削性に優れたワークロールを製造する場合には、製造及び使用時に大根割れ（胴部芯材内部を起点とする折損）等の不都合を生じさせないために、外層成分の芯材溶湯への混合希釈による芯材の白銑化及び脆弱化を防止する必要がある。
【００６３】
図１は、３．５ ％Ｃ−２．１ ％Ｓｉ−０．５ ％Ｍｎ−０．９ ％Ｎｉ−０．２ ％Ｍｏ−０．０３％Ｍｇ系の球状黒鉛鋳鉄に、Ｃｒ及びＶを （Ｃｒ＋２Ｖ） 量が１．０ ％以下の範囲で添加した時の（Ｃｒ＋２Ｖ） 量と硬さとの関係をラボテストにより調査した結果を示すグラフである。同図に示すように、球状黒鉛鋳鉄は （Ｃｒ＋２Ｖ） 量に比例して白銑化し、（Ｃｒ＋２Ｖ） 量が０．７０％を超えると著しく硬化すなわち脆弱化する。
【００６４】
したがって、本発明にかかる冷間圧延用遠心鋳造製複合ワークロールの熱処理法として、軸心部の引張残留応力を低くできるとともに、芯材の強靱性の劣化を防止することが可能である定置誘導加熱法を採用する場合においても、焼き入れ中の内部破断、さらには使用時の大根割れを防止するためには、両軸部の （Ｃｒ＋２Ｖ） 量を０．７０％以下に抑制する。好ましくは０．６５％以下に抑制する。
【００６５】
（実施例３）
遠心鋳造法は、鋳造機の回転軸の方向（傾斜角）で横型（傾斜角が０ 度）、傾斜型と竪型（傾斜角が９０度）とに分類され、日本においては横型あるいは傾斜型が多く用いられているのに対し、ヨーロッパ、米国等の日本を除く諸外国では竪型遠鋳機が用いられているので、前述の特許文献１で提案された高Ｃｒ鋳鋼を外層とする冷間圧延用遠心鋳造製複合ワークロールロールは竪型遠鋳機にて鋳造されていると推量される。このようなことから、傾斜角が異なった場合の本発明にかかる冷間圧延用遠心鋳造製複合ワークロールへの適用可否を検討した。
【００６６】
図２は、内径、長さがそれぞれ５６５ ｍｍ、２６００ ｍｍ であるモールドを用いて、芯材の鋳込み時の鋳込み側（あるいは鋳型の上側）のモールド端から２００ｍｍ 位置における溶湯厚みが６２ ｍｍ になるように外層材の溶湯を鋳込んだ時の、鋳造機の回転軸の傾斜角および遠心力の大きさ（重力加速度、Ｇ Ｎｏ． ）とモールド両端部間における溶湯厚みの差との関係を示すグラフである。
【００６７】
傾斜角が３０度以下であれば１２０Ｇの遠心力であってもモールド両端部間における溶湯厚みの差は１５ｍｍ以下となり、芯材溶湯鋳込み時の外層と芯材との溶着接合条件をモールド全長内でほぼ一定にすることができ、胴部全長に亘って健全な境界部を得ることができる。それに対して、傾斜角が３０度を超えると、芯材溶湯鋳込み時の外層厚みの差が大となり、胴部全長に亘って健全な境界部を得ることができなくなる。
【００６８】
特に、竪型では、外層内の半径方向の成分分布が不均一になる不具合を無視して、１６０Ｇの大きな遠心力を加えてもモールド両端部間における溶湯厚みの差は２０ｍｍを超えるので、外層が完全に凝固した状態でモールド中央から下部の接合条件に合わせて芯材溶湯を鋳込んだ場合には、溶湯厚みの小な芯材鋳込み側のモールド上端部は温度が下がり過ぎて溶着不良となる。一方、溶湯厚みが小さな芯材鋳込み側のモールド上端部に接合条件を合わせて芯材溶湯を鋳込んだ場合には、モールド中央から下部は凝固が完了していないので、Ｃｒ、Ｍｏ、Ｖ、Ｗ等の白銑化傾向が強い元素が多量に含有した、多量の未凝固溶湯が芯材溶湯中に混入して芯材を著しく白銑化し、熱処理中および／または使用中に芯材を起点とした内部破壊が発生する。このような不具合は、程度の差異はあるものの、傾斜角が３０度を超えた遠心鋳造機を用いた場合にも発生する。
【００６９】
なお、外層内面の未凝固溶湯および／または外層内面側に凝固形成された除去すべき外層の芯材溶湯への混合希釈による芯材の白銑化及び脆弱化を低減する手段として、芯材の鋳込み量を増加させる手段もあり得るが、これは製造コストの大幅なアップを招くため、本発明にかかる冷間圧延用遠心鋳造製複合ワークロールの目的にはそぐわず、好ましくない。
【００７０】
以上のことから、外層にＣｒ、Ｍｏ、Ｖ、Ｗ等の白銑化傾向の強い元素を多量に含有し、かつ胴部全長に亘って健全な境界部が要求される本発明にかかる冷間圧延用遠心鋳造製複合ワークロールの製造においては、遠心鋳造機の回転軸の傾斜角が３０度以下の遠心鋳造機、好ましくは２５度未満の遠心鋳造機を用いる。また、傾斜角が小さいほどモールド両端部間における溶湯厚みの差が小さくなるが、横型では、外層溶湯のモールド内への充填に要する時間が長くなり、外層の凝固組織に胴長方向のムラが生じやすくなるので、傾斜角は５ 度以上であることが好ましい。
【００７１】
（実施例４）
本発明例として、回転軸の傾斜角が１８度の傾斜型遠心鋳造機を用いて、製品時の胴部の直径５６０ｍｍ 、長さ２０３２ｍｍの複合ロールを製造した。この複合ロールは、以下に示す手順▲１▼〜▲４▼により製造した。
【００７２】
▲１▼胴部を形成するためのモールド（内径５９５ｍｍ 、長さ２６００ｍｍ）と両軸部を形成するための軸鋳型とを組み立てた後（組み立てたものを鋳型という）、遠心鋳造機に搭載した。なお、モールド内面には２ｍｍ厚さの塗型を施工した。
【００７３】
▲２▼モールド内面の遠心力が１２０Ｇになるように鋳型を高速回転させてから、低周波誘導炉を用いて溶解した、表３に示す化学組成の溶湯を外層材溶湯として、モールド長さ方向の中央位置の厚みが７２ｍｍになるように、モールド内に１４１０℃で鋳込んだ。
【００７４】
【表３】

【００７５】
▲３▼外層材溶湯が凝固した後に遠心鋳造機の回転を停止し、鋳型を垂直に立て、芯材として表３に示す球状黒鉛鋳鉄溶湯を、外層溶湯鋳込開始から２７分経過後、１４２０℃で鋳込んだ。
【００７６】
▲４▼冷却、鋳型解体及び焼鈍後、得られた鋳放し品の胴部表面を直径５６８ｍｍ に旋削加工し、超音波探傷により外層の厚みおよび境界部健全性を調査した。また、両胴端部から試験片を採取し、これらの試験片を使用して境界部健全性及び芯材の白銑化状況を調査した。さらに、両軸部から試験片を採取し、これらの試験片を使用して芯材の白銑化状況及び化学組成を調査した。
【００７７】
なお、芯材鋳込みにより除去された外層の厚みは、収縮率を１．０１として算出した。境界部の健全性は探触子５Ｚ２０Ｎ 、探傷感度 Ｖ１５−９０％＋２０ｄＢの条件で探傷し、反射エコーの高さ及び検出位置により判定した。芯材の内部の白銑化状況は、芯材のＣｒ、Ｖ量等の化学組成が両胴端部から採取した試験片内部の芯材と鋳込み時の下側軸部とでほぼ同一であったことから、芯材鋳込み時の下側軸部の化学組成により評価した。
【００７８】
超音波探傷により測定した外層厚みから算出した芯材鋳込みにより除去された外層の厚みは直径８ｍｍであり、かつ超音波探傷による境界部健全性は、境界部からの反射エコーの高さが１００ ％以下と良好であった。また、下側軸部から採取した試験片による芯材の（Ｃｒ＋２Ｖ） 量は０．４６％であり、芯材の白銑化は認められなかった。
【００７９】
このロールを焼き入れ寸法（胴長２０６０ｍｍ）に旋削加工した後、定置誘導加熱法により熱処理を行い、その後、胴部表面を旋削仕上加工して、超音波探傷により胴内部の健全性を調査した。
【００８０】
その結果、芯材の破断（内部破壊）もなく、所定の硬さであるショア硬さ９３が得られた。本発明例で実施した定置誘導加熱法は、次のようにして行った。ロール全体を４００ ℃に予熱保持した後、定置誘導加熱装置により胴部表面を平均昇温速度６５０ ℃／ｈで１０８５℃まで昇温し、この温度で７分間保持した後、噴霧を付加した衝風空気焼入れを行い、５２０ ℃の温度で停止する。続いてロール温度を５２０ ℃に２０時間維持し、次に空冷によりロールを室温まで冷却する。引き続き、このロールを５２０ ℃の温度で２０時間の焼き戻しを２回行った。
【００８１】
なお、特許文献１により開示された、高Ｃｒ鋳鋼を外層とする冷間圧延用遠心鋳造製複合ワークロールでは全体加熱焼き入れ法を採用しているが、この加熱法では、芯材が外層と同一の温度に加熱されるので、熱応力型の軸心部引張残留応力が大になり、かつ芯材が脆弱化し熱処理時および／または使用中に内部破壊が生じる可能性が高いとともに、芯材の溶融開始温度以上に焼き入れ温度を高くすることができないので、本発明ロールにおいてショア硬さ９０以上の高硬度を得るに必要な１０５０℃超の焼き入れ温度とすることができないために、本発明の遠心鋳造製複合ロールの熱処理には採用できない。
【００８２】
一方、前述の全体加熱焼き入れ法および本発明の定置誘導加熱法の他に、遠心鋳造製複合ロールの熱処理法としては、ガスバーナー等により胴部表面を焼き入れ温度に加熱する方法もある。しかしながら、この加熱法には、焼き入れ加熱域を確保するために必要以上にロール表面温度を上げる必要があるので、外層表面の溶融が生じやすいこと、また加熱速度が遅く芯材の温度が高くなるので、熱応力型の軸心部引張残留応力が大になること、及び芯材が脆弱化する等の不具合があること等により、本発明にかかる冷間圧延用遠心鋳造製複合ワークロールの熱処理には採用できない。
【００８３】
本発明の定置誘導加熱法によれば、外層の有効使用径域を適正な焼き入れ加熱温度に保持でき、かつ内部の温度が低く、焼き入れ冷却時には内部からの冷却も寄与するので、特に外層内部（径小域）の硬化が容易であるという特徴を有している。さらに、残留応力の観点からも、加熱速度が速く芯材の温度を低く抑える、すなわち軸心部の引張残留応力を低くできるとともに、芯材の強靱性の劣化を防止することが可能であり、本発明の遠心鋳造製複合ロールの熱処理法として好適である。
【００８４】
【発明の効果】
以上詳細に説明したように、本発明にかかる冷間圧延用遠心鋳造製複合ワークロールによれば、製造コストが安価で、かつエレクトロスラグ溶解法を用いた１０％Ｃｒ系あるいはセミハイス系の鍛鋼製焼き入れワークロールと同等かそれ以上の耐摩耗性および研削性を有する冷間圧延用複合ワークロールが提供される。
【００８５】
かかる効果を有する本発明の意義は著しい。
【図面の簡単な説明】
【図１】３．５ ％Ｃ−２．１ ％Ｓｉ−０．５ ％Ｍｎ−０．９ ％Ｎｉ−０．２ ％Ｍｏ−０．０３％Ｍｇ系の球状黒鉛鋳鉄に、Ｃｒ及びＶを （Ｃｒ＋２Ｖ） 量が１．０ ％以下の範囲で添加した時の （Ｃｒ＋２Ｖ） 量と硬さとの関係をラボテストにより調査した結果を示すグラフである。
【図２】内径、長さがそれぞれ５６５ ｍｍ、２６００ ｍｍ であるモールドを用いて、芯材の鋳込み時の鋳込み側のモールド端から２００ｍｍ 位置における溶湯厚みが６２ ｍｍ になるように外層材の溶湯を鋳込んだ時の、鋳造機の回転軸の傾斜角および遠心力の大きさ（重力加速度、Ｇ Ｎｏ． ）とモールド両端部間における溶湯厚みの差との関係を示すグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a centrifugally cast composite work roll for cold rolling that can be suitably used as a work roll for cold rolling of a metal material such as steel.
[0002]
[Prior art]
Conventionally, as a work roll for performing cold rolling of a metal material such as iron and steel, 5% (hereinafter, "%" means "% by mass" unless otherwise specified in this specification) A quenched work roll made of a Cr-based forged steel is frequently used. In particular, when abrasion resistance is required, a quenched work roll made of a forged steel made of a 10% Cr-based material corresponding to a cold die steel or a semi-high-speed forged steel added with a small amount of Mo, V, or the like is used. .
[0003]
These quenched work rolls made of forged steel are forged and annealed to steel ingots manufactured by the atmospheric melting method or the electroslag melting method, machined to predetermined shapes and dimensions, and then fixed induction heating quenching or continuous. Hardened to a desired hardness by moving induction heating and quenching. Here, “stationary induction heating quenching” is a quenching method in which the surface of the roll body is induction-heated to one side using a coil having a length covering the entire roll body, and then quenched. The “quenching” is a quenching method in which a coil shorter than the length of the roll body is quenched while moving from the lower part to the upper part of the body piece.
[0004]
The 10% Cr-based and semi-high-speed forged steel quenched work rolls disperse hard carbide formed by Cr, Mo, and V in steel to improve wear resistance. In addition to the inevitable waste that these expensive elements are contained in the entire ingot, that is, the part that does not directly contact the rolled material, the soundness inside the ingot cannot be secured only by the atmospheric melting method. Therefore, it is essential to use the electroslag melting method, and furthermore, since it is difficult to forge, the number of forging steps is increased. Therefore, the manufacturing cost is remarkably higher than that of a quenched work roll made of 5% Cr-based forged steel. There was a problem of being bulky.
[0005]
On the other hand, in Europe, from the early 1980's, after forming a high Cr cast iron (2.7% C-18% Cr) molten metal as an outer layer using a vertical centrifugal caster, inexpensive flake graphite cast iron or A centrifugally cast composite roll in which a spheroidal graphite cast iron melt is cast as a core material and welded and solidified is partially used as a work roll for cold rolling. Patent Literature 1 proposes a centrifugally cast composite work roll for cold rolling in which high Cr cast steel is used as the outer layer instead of high Cr cast iron.
[0006]
These centrifugally cast composite work rolls are obtained by machining an annealed cast product into a predetermined shape and dimensions, and then hardening the surface of the outer layer by overall heat quenching. Here, the entire heating and quenching is a method of quenching after gradually heating the entire roll to a quenching temperature so as not to have an excessive temperature gradient inside the roll body. Therefore, it is considered that the production cost is inexpensive, and if the required performance is ensured, it can surpass 10% Cr-based or semi-high-speed forged steel quenched work roll produced by the electroslag melting method.
[0007]
However, a centrifugal casting composite roll having a high Cr cast iron or a high Cr cast steel as an outer layer, which is manufactured using a vertical centrifugal caster and a horizontal or inclined centrifugal caster awarded in Japan, will be described later. Due to such problems in production and use performance, the fact is that in the cold rolling mills in Japan, they have hardly been used since the early 1990s.
[0008]
Furthermore, in recent years, as an alternative to these centrifugally cast composite work rolls, a core material such as a low-carbon low-alloy forged steel and the like, which contains a large amount of Cr, Mo, V, W, etc., and has excellent wear resistance. Patent Literature 2 or Patent Literature 3 proposes a technique for manufacturing a composite work roll for cold rolling in which the outer layer is formed by a build-up method using an electroslag remelting method or a continuous casting build-up method. The composite work rolls formed by these overlaying methods perform ingots formed by the overlaying method, and in some cases, also perform forging processing, process them into a predetermined shape and dimensions, and then continuously move induction heating and quenching to form the outer layer surface. Is to be cured.
[0009]
[Patent Document 1]
Japanese Patent Publication No. 1-1707
[Patent Document 2]
Japanese Patent Publication No. 7-68588
[Patent Document 3]
JP-A-10-27761
[0010]
[Problems to be solved by the invention]
However, the composite rolls formed by these overlaying methods have a high production cost because it is necessary to produce a core material such as a low-carbon low-alloy forged steel in advance. For this reason, the actual situation is that the use performance evaluation in consideration of the manufacturing cost does not surpass the forged steel quenching roll.
[0011]
Here, most of the work rolls for cold rolling of metal materials such as iron and steel are small diameter rolls having a body diameter of 650 mm or less, and the body surface hardness is selected in a range of 90 or more in Shore hardness. Have been. This is because, if the hardness is too low, inconveniences such as flaws are likely to occur due to the intrusion of dissimilar materials during use of rolling (the flaw resistance is referred to as “dent resistance”). In addition, since the work roll directly contacts the rolled material and greatly affects the dimensional accuracy and surface quality of the rolled product, wear resistance is strongly required, and the grindability that determines the surface quality of the work roll itself is also important. Required performance. Therefore, as a work roll material excellent in both abrasion resistance and grindability, hard carbide formed by elements such as Cr, Mo, V, and W is dispersed in a large amount in steel while considering grindability. It is necessary to improve the wear resistance.
[0012]
However, after forming a molten metal containing a large amount of elements forming hard carbides such as Cr, Mo, V, and W as an outer layer by centrifugal casting, the molten spheroidal graphite cast iron is cast as a core material and welded and joined. It is not practically possible to produce a centrifugally cast composite work roll with an outer layer surface hardened to a Shore hardness of 90 or more and excellent in abrasion resistance by coagulation. It is supposed to be.
[0013]
First, the centrifugal casting composite roll solidifies the outer layer material melt from the mold surface to the inside under a large centrifugal force, so the concentrated melt or primary carbide on the solidification front, which differs in specific gravity from the melt, migrates through the unsolidified melt. As a result, the component distribution in the radial direction in the solidified outer layer tends to be non-uniform, and a hard or brittle carbide-enriched layer or a hypereutectic composition phase that is difficult to weld and bond is formed inside the outer layer. May be easier to do. This phenomenon becomes more remarkable as the outer layer material melt contains a larger amount of elements such as Cr, Mo, V, and W, and as the centrifugal force used increases.
[0014]
On the other hand, it is necessary to increase the centrifugal force to minimize the difference in the thickness of the molten metal in the length direction of the mold as much as possible in order to keep the welding conditions of the outer layer and the core material constant during the casting of the molten core material. Since the centrifugal force is proportional to the square of the rotation speed and the diameter, the smaller the inner diameter of the mold (after all, the diameter of the roll body) and the thicker the outer layer material melt, the more the centrifugal force is required to obtain a sound boundary. You need to increase your power.
[0015]
Therefore, in particular, in a work roll for cold rolling in which a small-diameter roll having a diameter of 650 mm or less occupies most, if the difference in the thickness of the molten metal in the mold is reduced in order to obtain a sound boundary portion, the radial component in the outer layer can be reduced. There is a disadvantage that the distribution becomes non-uniform, and a carbide-enriched layer or a hypereutectic composition phase, which is difficult or fragile to be welded and joined, is easily formed inside the outer layer. Conversely, if the centrifugal force is suppressed to make the radial component distribution in the outer layer uniform, the difference in the thickness of the molten metal in the mold becomes large, and there is a disadvantage that it is difficult to secure a sound boundary portion. .
[0016]
Spheroidal graphite cast iron, which forms the core material of a composite roll by centrifugal casting, can exhibit toughness by crystallizing graphite, but the outer layer is made of white iron such as Cr, Mo, V, W, etc. When a large amount of an element having a strong tendency to form is contained, there is a problem that the graphitization of the core material is inhibited and the core material is apt to become brittle. That is, when unmelted molten metal remains on the inner surface of the outer layer during casting of the molten core material, the unsolidified molten metal is mixed with the molten core material and diluted into the molten molten core material. In addition, since the brittle carbide-enriched layer or the hypereutectic composition phase is concentrated on the inner surface side of the solidified outer layer as described above, it is necessary to melt and remove these with a molten core material. is there.
[0017]
Furthermore, when a high melting point material having a low C content is used for the outer layer in consideration of the grinding property, casting defects such as shrinkage cavities are likely to occur inside the solidified outer layer. It is necessary to melt and remove the core material. Therefore, the degree of the white iron and the brittleness of the core material is determined by the thickness (amount) of the unsolidified molten metal on the inner surface of the outer layer and / or the outer layer to be removed solidified on the inner surface side of the outer layer, and Cr, Mo, It is determined by the amount of elements having a strong tendency to form white iron, such as V and W.
[0018]
For this reason, particularly, the present invention is intended to contain a large amount of elements having a strong tendency to form white iron, such as Cr, Mo, V, and W, and to easily generate casting defects such as shrinkage cavities on the inner surface side. When manufacturing a work roll with a high melting point material as the outer layer and the surface of the outer layer hardened to a Shore hardness of 90 or more and excellent in wear resistance and grinding properties, the welding strength of the outer layer and the core material is significantly reduced. If it is intended to completely remove a casting defect such as a carbide-enriched layer or shrinkage cavities, there is a problem that the iron core is apt to be made of white iron and brittleness, and the actual situation is that practical use has not been advanced.
[0019]
On the other hand, it has been proposed to provide an intermediate layer such as adamite or graphite steel between the outer layer and the core material as a means for reducing white iron and brittleness of the core material by mixing and diluting the outer layer component into the molten core material. I have. However, in this method, the mixed and melted outer layer components are mixed and diluted in the intermediate layer, and the formed intermediate layer has similar thermomechanical properties to the outer layer, and as a result, the used layer of the roll becomes Means that the thickness of the outer layer that cannot be used is simply increased. For this reason, in this method, a work roll, in which the surface of the outer layer is hardened to a Shore hardness of 90 or more and whose diameter is 650 mm or less and which is mostly composed of 650 mm or less, breaks radish during production and use as described later. (Breakage originating from the inside of the trunk core material) and the like.
[0020]
Next, the centrifugal casting composite work roll using spheroidal graphite cast iron as a core material has a large problem with respect to heat treatment.
During quenching of the composite roll, a large compressive residual stress is generated in the outer layer due to transformation expansion, and a large tensile stress is generated in the core material in balance with the residual stress, which is quenched when the tensile strength exceeds the tensile strength of the core material. The core material breaks inside. This problem is more likely to occur as the diameter of the roll body becomes smaller, that is, as the cross-sectional area of the outer layer occupying the cross-sectional area of the roll body becomes relatively larger, because the tensile stress generated in the core material increases. In addition, as the surface of the outer layer is hardened, that is, as the cooling rate at the time of quenching cooling is increased, not only the transformation expansion of the outer layer is increased, but also the temperature gradient inside the roll body is increased, which acts on the core material. Since the tensile stress of the thermal stress type increases, the problem that the core material breaks during quenching tends to occur.
[0021]
Therefore, small-diameter rolls having a diameter of 650 mm or less occupy the majority, and the outer layer contains a large amount of elements such as Cr, Mo, V, W, etc., which have a strong tendency to form white pig iron, thereby causing white iron and weakening of the core material. When manufacturing a work roll excellent in abrasion resistance and grindability in which the surface of the outer layer is easily hardened to a Shore hardness of 90 or more, the entire layer is heated and quenched to generate on the core material during quenching and cooling. Even if the stress is not excessive, there is a problem that the core material breaks during quenching.
[0022]
In addition, when continuous induction heating quenching is applied to a centrifugally cast composite work roll, quenching heating and cooling are performed in a continuously moving manner from the lower part of the body piece to the upper part. There is a problem that cracks occur in the outer layer from the surface of the starting portion, and there is a problem that the core material is rapidly heated locally and the core material is broken during quenching.
[0023]
Furthermore, as one of the reasons why the centrifugal casting cold roll composite roll using high Cr cast iron as the outer layer did not spread in Japanese cold rolling mills, the grindability was lower than that of a 5% Cr based forged steel quenched roll. In some cases, use problems such as badness are likely to occur. In order to solve this problem, Patent Literature 1 proposes a vertical centrifugal casting cold rolling composite roll having a high Cr cast steel as an outer layer instead of the high Cr cast iron. The fact is that progress has not been made. This is because the high Cr cast steel disclosed in Patent Literature 1 cannot meet recent needs for high quality of rolled products.
[0024]
The present invention is to solve the above-described problem that occurs when applying a centrifugally cast composite roll to a work roll for performing cold rolling of a metal material such as iron and steel. A high-performance cold-rolled centrifugally cast composite work roll that is less expensive to manufacture than the used 10% Cr-based or semi-high-speed forged steel quenched work roll and has equal or better wear resistance and grindability. To provide.
[0025]
[Means for Solving the Problems]
The present invention is a composite roll provided with an outer layer formed by a centrifugal caster having an inclination angle of a rotating shaft of 30 degrees or less and a core material made of spheroidal graphite cast iron, wherein the outer layer has a C: 0.50-0. 0.95%, Si: 0.2 to 2.0%, Mn: 0.2 to 2.0%, Ni: 0.1 to 2.0%, Cr: 4.5 to 8.5%, Mo: It is an iron-based high alloy that satisfies 1.5 to 4.5%, V: 0.1 to 1.0%, and W: 0.1 to 3.0%. The (Cr + 2V) content of graphite cast iron is 0.70% or less, and the surface of the outer layer is hardened to a Shore hardness of 90 or more by stationary induction heating and quenching. It is a centrifugally cast composite work roll for rolling.
[0026]
Further, the present invention is a composite roll comprising an outer layer formed by a centrifugal casting machine having an inclination angle of a rotating shaft of 30 degrees or less and a core material made of spheroidal graphite cast iron, wherein the outer layer has a C: 0.50 0.9 to 0.95%, Si: 0.2 to 2.0%, Mn: 0.2 to 2.0%, Ni: 0.1 to 2.0%, Cr: 4.5 to 8.5%, Mo: 1.5 to 4.5%, V: 0.1 to 1.0%, W: 0.1 to 3.0%, and {C + 0.1 (Cr + 0.8Mo + 0.4W)} amount. It is an iron-based high alloy that satisfies 1.70% or less, the (Cr + 2V) amount of the spheroidal graphite cast iron constituting the both shafts of this roll is 0.70% or less, and the surface of the outer layer is fixed by induction heating. Centrifugal casting for cold rolling with excellent wear resistance and grindability characterized by being hardened to a Shore hardness of 90 or more by putting A composite work roll.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the reasons for limiting the main composition of the iron-based high alloy constituting the outer layer of the body of the centrifugally cast composite work roll for cold rolling according to the present invention will be described.
[0028]
C: 0.50 ~ 0.95 %
C forms a hard carbide by forming a solid solution in the matrix to enhance the quenchability and combining with elements such as Cr, Mo, V, and W. However, if the content is less than 0.50%, the amount of carbides is small, and wear resistance cannot be obtained. On the other hand, if the content exceeds 0.95%, the amount of carbides increases and the grindability deteriorates. Therefore, the range of the C content is limited to 0.50% or more and 0.95% or less. From the same viewpoint, it is preferable that the lower limit of the C content is 0.55% and the upper limit is 0.90%.
[0029]
Si : 0.2 ~ 2.0 %
Si is added for the purpose of deoxidation. However, if the Si content is less than 0.2%, the effect is insufficient. Conversely, if the Si content is more than 2.0%, micro segregation is promoted to deteriorate the grindability. Therefore, the range of the Si content is limited to 0.2% or more and 2.0% or less.
[0030]
Mn : 0.2 ~ 2.0 %
Mn is added for the purpose of deoxidation and desulfurization. However, if the Mn content is less than 0.2%, the effect is insufficient. On the other hand, if the Mn content exceeds 2.0%, the toughness is reduced. % To 2.0% or less.
[0031]
Ni : 0.1 ~ 2.0 %
Ni improves the quenchability by forming a solid solution in the matrix. Therefore, Ni is contained in an amount of 0.1% or more. However, if the Ni content exceeds 2.0%, the retained austenite is excessively stabilized, and it is difficult to secure hardness. Therefore, the range of the Ni content is limited to 0.1% or more and 2.0% or less. From the same viewpoint, it is preferable that the lower limit of the Ni content is 0.2% and the upper limit is 1.5%.
[0032]
Cr : 4.5 ~ 8.5 %
Cr forms a solid Cr carbide by forming a solid solution in the matrix to enhance and strengthen hardenability and combine with C. If the Cr content is less than 4.5%, these effects are small. Conversely, if the Cr content exceeds 8.5%, the amount of carbides increases and the grindability deteriorates. Therefore, the range of the Cr content is limited to 4.5% or more and 8.5% or less. From the same viewpoint, the lower limit of the Cr content is desirably 5.0%, and the upper limit is desirably 8.0%.
[0033]
Mo : 1.5 ~ 4.5 %
Like Mo, Mo also forms a solid solution in the matrix to enhance and harden hardenability, and also combines with C to form a hard carbide. Therefore, the content is increased to 1.5% or more for strengthening the base. However, when the content exceeds 4.5%, the amount of carbide increases and the grindability deteriorates. Therefore, the range of the Mo content is limited to 1.5% or more and 4.5% or less. From the same viewpoint, the lower limit of the Mo content is 2. The upper limit is desirably 0%, and the upper limit is desirably 4.0%.
[0034]
V: 0.1 ~ 1.0 %
V is an important element that combines with C to form the hardest MC carbide. However, if the content is less than 0.1%, the amount of carbides is insufficient and the wear resistance cannot be secured. MC carbides increase to deteriorate the grindability. Therefore, the range of the V content is limited to 0.1% or more and 1.0% or less.
[0035]
W: 0.1 ~ 3.0 %
W, like Mo, forms a solid solution in the matrix to enhance and strengthen hardenability, and combines with C to form a hard carbide. In order to strengthen the base, the content is at least 0.1% or more, but if it exceeds 3.0%, the amount of carbides increases and the grindability deteriorates. Therefore, the range of the W content is limited to 0.1% or more and 3.0% or less. From the same viewpoint, it is preferable that the lower limit of the W content is 0.2% and the upper limit is 2.5%.
[0036]
｛C + 0.1 (Cr + 0.8Mo + 0.4 W) Quantity: 1.70 %Less than
The grindability deteriorates in proportion to the amount of {C + 0.1 (Cr + 0.8Mo + 0.4 W)}. If this value exceeds 1.70%, it becomes difficult to secure good roll surface properties. The amount of {C + 0.1 (Cr + 0.8Mo + 0.4 W)} is limited to 1.70% or less. From the same viewpoint, the upper limit of the amount of {C + 0.1 (Cr + 0.8Mo + 0.4 W)} is desirably limited to 1.65%.
[0037]
The iron-based high alloy constituting the outer layer of the body of the centrifugally cast composite work roll for cold rolling according to the present invention may be obtained by adding Nb, Co, Ti, etc., in addition to the main chemical components described above. The appropriateness and content of the addition may be appropriately determined in consideration of wear resistance, grinding property, and the like.
[0038]
Next, an example of the main chemical components of the spheroidal graphite cast iron which is the core material constituting the inside of the body and both shafts of the centrifugally cast composite work roll for cold rolling according to the present invention will be briefly described.
[0039]
C: 2.5 ~ 3.6 %
If the content of C is less than 2.5%, the amount of graphite decreases, and the material properties as spheroidal graphite cast iron cannot be sufficiently exhibited. On the other hand, if it exceeds 3.6%, it becomes fragile. Therefore, in the present embodiment, the C content is 2.5% or more and 3.6% or less.
[0040]
Si : 1.6 ~ 3.3 %
If the content of Si is less than 1.6%, the amount of graphite is reduced and carbides are precipitated in a large amount, so that Si becomes brittle. On the other hand, if it exceeds 3.3%, the amount of graphite becomes too large, resulting in deterioration of strength. Therefore, in the present embodiment, the Si content is limited to 1.6% or more and 3.3% or less.
[0041]
Mn : 0.2 ~ 0.8 %
Mn is effective in suppressing the harm of S, but if it is less than 0.2%, its effect is not sufficient, and if it exceeds 0.8%, the material deteriorates. Therefore, in the present embodiment, the Mn content is limited to 0.2% or more and 0.8% or less.
[0042]
P: 0.1 %Less than
Although P increases the fluidity of the molten metal, it makes the material brittle, so in the present embodiment, it is limited to less than 0.1%.
[0043]
S: 0.05 %Less than
S must be kept low in order to inhibit spheroidization of graphite. In the present embodiment, the S content is limited to less than 0.05%.
[0044]
Ni : 0.2 ~ 1.5 %
Ni promotes graphitization, but its effect is insufficient when the Ni content is less than 0.2%, while there is no significant effect when the Ni content exceeds 1.5%. Therefore, in the present embodiment, the range of the Ni content is 0.2% or more and 1.5% or less.
[0045]
Mg : 0.02 ~ 0.08 %
Mg has an effect of promoting spheroidization of graphite. However, if the content is less than 0.02%, the effect is insufficient. On the other hand, if the content exceeds 0.08%, graphitization is inhibited, and casting defects are easily generated. Therefore, in the present embodiment, it is limited to 0.02% or more and 0.08% or less.
[0046]
Cr , Mo , V, W: each 0.70% Below and ( Cr + 2V) 0.70 %Less than
Since Cr, Mo, V, and W are elements of white iron as described above, they are not basically added to the molten spheroidal graphite cast iron for forming the core material of the present invention. However, since the outer layer of the composite roll of the present invention contains a large amount of Cr, Mo, V, and W, when the outer layer and the core material are welded and joined, the elements contained in those outer layers are inevitable in the core material. Mixed. Moreover, it may be inevitably mixed from the dissolved raw material. If any of these are mixed in the core material, the spheroidization of the graphite in the core material is inhibited, and the iron material becomes white and brittle. Therefore, the upper limits of the contents of Cr, Mo, V, and W are each set to 0.70%.
[0047]
Further, with respect to Cr and V, which are strong white iron-forming elements, when the (Cr + 2V) amount exceeds 0.70%, even if heat treatment employing the stationary induction heating and quenching method is performed, destruction from the inside of the core material will occur. Therefore, the amount of (Cr + 2V) is limited to 0.70% or less. From the same viewpoint, the upper limit of the amount of (Cr + 2V) is desirably 0.65%.
[0048]
Further, spheroidal graphite cast iron, which is a core material constituting the inside of the body and both shafts of the centrifugally cast composite work roll for cold rolling according to the present invention, further contains Nb, Co, In some cases, elements contained in the outer layer such as Ti are inevitably mixed, but it is preferable to appropriately judge the appropriateness of the mixing in consideration of the spheroidization of the graphite, the formation of white pig iron, the brittleness, and the like.
[0049]
The outer layer of the centrifugally cast composite work roll for cold rolling according to the present invention is formed by a centrifugal casting machine in which the inclination angle of the rotating shaft is 30 degrees or less. If the inclination angle of the rotating shaft is more than 30 degrees, the welding and joining conditions between the outer layer and the core material during the casting of the molten core material cannot be made substantially constant within the entire length of the mold, and soundness is maintained over the entire length of the body. This is because not only a boundary portion cannot be obtained, but also whitening of the core material is apt to occur, and breakage is likely to occur during heat treatment and / or during use.
[0050]
Furthermore, the surface of the outer layer of the centrifugally cast composite work roll for cold rolling according to the present invention is hardened to a Shore hardness of 90 or more by stationary induction heating and quenching. In this stationary induction heating and quenching, the effective use diameter range of the outer layer can be maintained at an appropriate quenching heating temperature, the internal temperature is low, and cooling during quenching contributes to cooling from the inside. (Small area) is easy to cure. Furthermore, from the viewpoint of residual stress, it is possible to reduce the temperature of the core material at a high heating rate, that is, to reduce the tensile residual stress at the shaft center, and to prevent deterioration of the toughness of the core material, It is suitable as a heat treatment method for the centrifugally cast composite roll of the present invention.
[0051]
Further, the configuration of the centrifugally cast composite work roll for cold rolling according to the present invention will be described in detail along with its embodiments.
[0052]
【Example】
(Example 1)
Forging and quenching work rolls made of 5% Cr-based forged steel and quenched work rolls made of semi-high-speed forged steel (electro-slag melting method), which have the chemical components shown in Table 1 and are manufactured in a normal process. Various compositions including two types of conventional materials collected from the body end after annealing and high Cr cast steel (comparative material 1) smelted by a resistance melting furnace and cast by a small centrifugal casting tester (mold inner diameter 120mm) From the material (Comparative materials 2 to 4) and the material of the present invention, a rotating wear test piece and a test piece for grinding evaluation (diameter 90 mm) were collected. These test pieces were adjusted to a Shore hardness of 91 to 96 by quenching from 970 to 1085 ° C. and further tempering at 100 to 520 ° C.
[0053]
[Table 1]

[0054]
In the rolling wear test, the mating material: a quenched work roll material made of 5% Cr-based forged steel having a Shore hardness of 93, lubrication: kerosene, surface condition: surface roughness Ra adjusted to 2 μm by grinding, Hertzian contact stress: 1451 MPa , Slip rate: 5%, rotation speed: 2 × 10⁵The test was performed under the same conditions, and the loss on wear was measured.
[0055]
Table 1 shows the wear loss of the material of the present invention, the conventional material and the comparative material by the rotational wear test. As shown in Table 1, the material of the present invention has less abrasion loss than the conventional material and the comparative material. In particular, the comparative material 1 and the comparative material 4 have a higher Cr content than the material of the present invention, but have a large amount of wear loss. That is, adding V and W in combination with Mo is more effective for improving wear resistance than adding a large amount of Cr.
[0056]
As described above, when the material of the present invention is applied to the outer layer material of the composite work roll for cold rolling, it is apparent that the intended function and effect of wear resistance are sufficiently exhibited.
The grindability evaluation test was performed using a general-purpose grindstone (WA120) having a diameter of 355 mm under conditions simulating the actual grinding of a work roll for cold rolling, and the surface condition after grinding (finished roughness and chattering). (Occurrence or non-occurrence).
[0057]
Table 2 shows the relationship between the {C + 0.1 (Cr + 0.8Mo + 0.4 W)} amount of the conventional material, the comparative material, and the material of the present invention, the finished roughness, and the occurrence of chatter.
[0058]
[Table 2]

[0059]
As is clear from this table, the material of the present invention having a {C + 0.1 (Cr + 0.8Mo + 0.4 W)} amount of 1.70% or less has a high finish roughness without generation of chatter even when a general-purpose grindstone is used. Can be ground every time. That is, when the amount of {C + 0.1 (Cr + 0.8Mo + 0.4 W)} is set to 1.70% or less, a polished grinding defect such as chattering and scratches can be generated to achieve a predetermined grinding roughness. Good grindability can be secured.
[0060]
On the other hand, the conventional material and the comparative material having the amount of {C + 0.1 (Cr + 0.8Mo + 0.4 W)} exceeding 1.70% generate chatter and have only a low finish roughness, resulting in poor grindability. It turned out to be inferior. That is, by suppressing the content of Cr, which greatly impairs grindability, and by adding Mo, V, and W in combination, it is possible to secure excellent wear resistance as well as excellent wear resistance.
[0061]
As described above, when the material of the present invention is applied to the outer layer material of the composite work roll made by centrifugal casting for cold rolling according to the present invention, it has a sufficient effect of being excellent in abrasion resistance and obtaining good grindability.
[0062]
(Example 2)
Rolls having a diameter of 650 mm or less occupy the majority, and the outer layer contains Cr, Mo, V, W, and other elements with a strong tendency to form white iron, so that the core material is apt to become white iron and become brittle. When manufacturing a work roll having an outer layer surface hardened to a Shore hardness of 90 or more and having excellent wear resistance and grindability, radish cracking during production and use (breakage starting from the inside of the body core material) In order to avoid such inconveniences as above, it is necessary to prevent white iron from becoming brittle and embrittlement of the core material due to mixing and dilution of the outer layer components into the molten core material.
[0063]
FIG. 1 shows that 3.5% C-2.1% Si-0.5% Mn-0.9% Ni-0.2% Mo-0.03% Mg-based spheroidal graphite cast iron was doped with Cr and V. It is a graph which shows the result of having investigated by a lab test the relationship between the amount of (Cr + 2V) and hardness when the amount of (Cr + 2V) was added in the range of 1.0% or less. As shown in the figure, the spheroidal graphite cast iron becomes white pig in proportion to the amount of (Cr + 2V), and becomes extremely hardened or brittle when the amount of (Cr + 2V) exceeds 0.70%.
[0064]
Therefore, as a heat treatment method of the centrifugally cast composite work roll for cold rolling according to the present invention, stationary induction that can reduce the tensile residual stress in the shaft center portion and prevent the toughness of the core material from deteriorating. Even when the heating method is employed, the amount of (Cr + 2V) in both shaft portions is suppressed to 0.70% or less in order to prevent internal breakage during quenching and radish cracking during use. Preferably, it is suppressed to 0.65% or less.
[0065]
(Example 3)
The centrifugal casting method is classified into a horizontal type (tilt angle is 0 degree), a tilt type and a vertical type (tilt angle is 90 degrees) according to the direction (tilt angle) of the rotation axis of the casting machine. In contrast to other countries such as Europe and the United States, except for Japan, vertical centrifugal casting machines are used. It is presumed that the composite work roll made of centrifugal casting for cold rolling is cast by a vertical centrifugal caster. From this, the applicability of the present invention to the centrifugally cast composite work roll for cold rolling according to the present invention when the inclination angle is different was examined.
[0066]
FIG. 2 shows that the thickness of the molten metal at a position 200 mm from the mold end on the casting side (or the upper side of the mold) at the time of casting the core material is 62 mm using molds having an inner diameter and a length of 565 mm and 2600 mm, respectively. Shows the relationship between the inclination angle of the rotating shaft of the casting machine and the magnitude of the centrifugal force (gravitational acceleration, G No.) when the molten metal of the outer layer material is cast as described above, and the difference in the molten metal thickness between both ends of the mold. It is a graph.
[0067]
If the inclination angle is 30 degrees or less, the difference in the thickness of the molten metal between both ends of the mold becomes 15 mm or less even at a centrifugal force of 120 G, and the welding and joining conditions between the outer layer and the core material during the casting of the molten core material are set within the entire length of the mold. , And a healthy boundary can be obtained over the entire length of the trunk. On the other hand, if the inclination angle exceeds 30 degrees, the difference in the thickness of the outer layer at the time of casting the core material becomes large, so that a sound boundary cannot be obtained over the entire length of the trunk.
[0068]
In particular, in the vertical type, the difference in the thickness of the molten metal between both ends of the mold exceeds 20 mm even when a large centrifugal force of 160 G is applied, ignoring the problem that the component distribution in the radial direction in the outer layer becomes non-uniform. When the molten core material is cast from the center of the mold to the lower joining condition in a state where it is completely solidified, the upper end of the mold on the side where the molten metal has a small thickness is cast too low, resulting in poor welding. Become. On the other hand, when the molten core material is cast at the upper end portion of the mold on the core material casting side where the thickness of the molten metal is small, the solidification is not completed from the center to the lower portion of the mold, so that Cr, Mo, V, A large amount of unsolidified molten metal containing a large amount of elements that have a strong tendency to form white iron, such as W, is mixed into the molten core material to significantly whiten the core material, and the starting material starts from the core material during heat treatment and / or during use. Internal destruction occurs. Such inconvenience also occurs when using a centrifugal casting machine having an inclination angle of more than 30 degrees although varying in degree.
[0069]
As means for reducing the whitening and brittleness of the core material by mixing and diluting the unsolidified molten metal on the inner surface of the outer layer and / or the molten core material of the outer layer to be removed solidified on the inner surface side of the outer layer, There may be a means for increasing the pouring amount, but this greatly increases the manufacturing cost, and therefore does not meet the purpose of the centrifugally cast composite work roll for cold rolling according to the present invention, which is not preferable.
[0070]
From the above, according to the present invention, the outer layer contains a large amount of elements having a strong tendency to form white iron, such as Cr, Mo, V, and W, and a sound boundary portion is required over the entire length of the body. In the production of the centrifugal casting composite work roll for rolling, a centrifugal casting machine in which the inclination angle of the rotation axis of the centrifugal casting machine is 30 degrees or less, and preferably a centrifugal casting machine with less than 25 degrees is used. In addition, the smaller the inclination angle, the smaller the difference in the thickness of the molten metal between both ends of the mold.However, in the case of the horizontal type, the time required for filling the outer layer molten metal into the mold is longer, and the solidification structure of the outer layer has unevenness in the body length direction. It is preferable that the inclination angle is 5 degrees or more, since this is likely to occur.
[0071]
(Example 4)
As an example of the present invention, a composite roll having a body diameter of 560 mm and a length of 2032 mm was manufactured using an inclined centrifugal casting machine in which the inclination angle of the rotating shaft was 18 degrees. This composite roll was manufactured by the following procedures (1) to (4).
[0072]
{Circle around (1)} After assembling a mold for forming the body (inner diameter 595 mm, length 2600 mm) and a shaft mold for forming both shafts (the assembled body is referred to as a mold), it was mounted on a centrifugal casting machine. . A mold having a thickness of 2 mm was applied to the inner surface of the mold.
[0073]
(2) The mold was rotated at a high speed so that the centrifugal force on the inner surface of the mold became 120 G, and then melted using a low-frequency induction furnace. Was cast at 1410 ° C. in a mold so that the thickness at the central position became 72 mm.
[0074]
[Table 3]

[0075]
(3) The rotation of the centrifugal casting machine was stopped after the outer layer material melt solidified, the mold was set upright, and a spheroidal graphite cast iron melt shown in Table 3 was used as a core material, and after 27 minutes from the start of the outer layer melt casting, 1420 Cast at ° C.
[0076]
{Circle over (4)} After cooling, mold disassembly and annealing, the body surface of the as-cast product obtained was turned to a diameter of 568 mm, and the thickness of the outer layer and the integrity of the boundary were examined by ultrasonic flaw detection. In addition, test pieces were collected from both body ends, and the soundness of the boundary and the state of white iron conversion of the core material were investigated using these test pieces. Furthermore, test pieces were collected from both shaft portions, and the state of white iron formation and the chemical composition of the core material were investigated using these test pieces.
[0077]
The thickness of the outer layer removed by casting the core material was calculated with a shrinkage factor of 1.01. The soundness of the boundary was detected under the conditions of a probe 5Z20N and a flaw detection sensitivity of V15-90% + 20 dB, and determined based on the height of the reflected echo and the detection position. Regarding the state of white pig iron inside the core material, the chemical composition such as the amount of Cr and V in the core material was almost the same between the core material inside the test piece collected from both body ends and the lower shaft part at the time of casting. Therefore, the evaluation was made based on the chemical composition of the lower shaft portion at the time of casting the core material.
[0078]
The thickness of the outer layer removed by casting the core calculated from the thickness of the outer layer measured by ultrasonic testing was 8 mm in diameter, and the integrity of the boundary by ultrasonic testing was such that the height of the reflected echo from the boundary was 100%. The following was good. The amount of (Cr + 2V) in the core obtained from the test piece taken from the lower shaft portion was 0.46%, and no white iron was found in the core.
[0079]
After turning the roll to a quenching dimension (body length of 2060 mm), heat treatment was performed by a stationary induction heating method, and then the body surface was turned and finished, and the soundness inside the body was examined by ultrasonic flaw detection. .
[0080]
As a result, there was no breakage (internal breakage) of the core material, and a predetermined hardness of Shore hardness 93 was obtained. The stationary induction heating method implemented in the examples of the present invention was performed as follows. After the entire roll was preheated and held at 400 ° C., the body surface was heated to 1085 ° C. at an average heating rate of 650 ° C./h by a stationary induction heating device, held at this temperature for 7 minutes, and then sprayed. Wind quench and shut off at a temperature of 520 ° C. Subsequently, the roll temperature is maintained at 520 ° C. for 20 hours, then the roll is cooled to room temperature by air cooling. Subsequently, the roll was tempered twice at a temperature of 520 ° C. for 20 hours.
[0081]
In addition, in the composite work roll made by centrifugal casting for cold rolling having a high Cr cast steel as the outer layer disclosed in Patent Document 1, the entire heating and quenching method is adopted. Since the cores are heated to the same temperature, the thermal stress-type axial residual stress at the axial center becomes large, and the core material becomes brittle, and there is a high possibility that internal destruction occurs during heat treatment and / or during use. Since the quenching temperature cannot be higher than the melting start temperature of the roll of the present invention, the quenching temperature of more than 1050 ° C. required for obtaining a high hardness of 90 or more in Shore hardness in the roll of the present invention cannot be obtained. It cannot be used for heat treatment of the centrifugally cast composite roll of the invention.
[0082]
On the other hand, in addition to the above-described overall heat quenching method and the stationary induction heating method of the present invention, as a heat treatment method for a centrifugally cast composite roll, there is a method of heating the body surface to a quenching temperature using a gas burner or the like. However, in this heating method, it is necessary to raise the roll surface temperature more than necessary to secure the quenching heating area, so that the outer layer surface is likely to be melted, and the heating speed is slow and the core material temperature is high. Therefore, due to the fact that the axial stress tensile residual stress of the thermal stress type becomes large and the core material becomes weak, etc., the centrifugally cast composite work roll for cold rolling according to the present invention. Cannot be used for heat treatment.
[0083]
According to the stationary induction heating method of the present invention, the effective use diameter range of the outer layer can be maintained at an appropriate quenching heating temperature, and the internal temperature is low. It has the feature that the inside (small diameter region) is easily cured. Furthermore, from the viewpoint of residual stress, it is possible to reduce the temperature of the core material at a high heating rate, that is, to reduce the tensile residual stress at the shaft center, and to prevent deterioration of the toughness of the core material, It is suitable as a heat treatment method for the centrifugally cast composite roll of the present invention.
[0084]
【The invention's effect】
As described above in detail, according to the centrifugally cast composite work roll for cold rolling according to the present invention, the production cost is low, and a 10% Cr-based or semi-high-speed forged steel made by electroslag melting is used. A composite work roll for cold rolling having wear resistance and grindability equal to or higher than that of a quenched work roll is provided.
[0085]
The significance of the present invention having such effects is remarkable.
[Brief description of the drawings]
FIG. 1 shows the addition of Cr and V to 3.5% C-2.1% Si-0.5% Mn-0.9% Ni-0.2% Mo-0.03% Mg based spheroidal graphite cast iron. It is a graph which shows the result of having investigated by a lab test the relationship between the amount of (Cr + 2V) and hardness when the (Cr + 2V) amount was added in the range of 1.0% or less.
FIG. 2 is a view showing a state in which the thickness of the molten metal at the position 200 mm from the mold end on the casting side when the core material is cast is set to 62 mm using molds having an inner diameter and a length of 565 mm and 2600 mm, respectively. Is a graph showing the relationship between the inclination angle of the rotating shaft of the casting machine and the magnitude of centrifugal force (gravitational acceleration, G No.) and the difference in the thickness of the molten metal between both ends of the mold when the casting is performed.

Claims (2)

A composite roll including an outer layer formed by a centrifugal casting machine having a rotation angle of 30 degrees or less and a core made of spheroidal graphite cast iron,
The outer layer is, by mass%, C: 0.50 to 0.95%, Si: 0.2 to 2.0%, Mn: 0.2 to 2.0%, Ni: 0.1 to 2.0%. %, Cr: 4.5 to 8.5%, Mo: 1.5 to 4.5%, V: 0.1 to 1.0%, and W: 0.1 to 3.0% High alloy,
The (Cr + 2V) content of the spheroidal graphite cast iron constituting both shaft portions of the roll is 0.70% or less, and the surface of the outer layer is hardened to a Shore hardness of 90 or more by stationary induction quenching. Centrifugal cast composite work roll for cold rolling with excellent wear resistance. A composite roll comprising an outer layer formed by a centrifugal casting machine having a rotation angle of 30 degrees or less and a core material made of spheroidal graphite cast iron,
The outer layer is, by mass%, C: 0.50 to 0.95%, Si: 0.2 to 2.0%, Mn: 0.2 to 2.0%, Ni: 0.1 to 2.0%. %, Cr: 4.5 to 8.5%, Mo: 1.5 to 4.5%, V: 0.1 to 1.0%, W: 0.1 to 3.0%, and ΔC + 0. 1 (Cr + 0.8Mo + 0.4 W)} is an iron-based high alloy satisfying 1.70% or less,
The (Cr + 2V) content of the spheroidal graphite cast iron constituting both shaft portions of the roll is 0.70% or less, and the surface of the outer layer is hardened to a Shore hardness of 90 or more by stationary induction quenching. Centrifugal casting composite work roll for cold rolling with excellent wear resistance and excellent grindability.

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